Jose Mourinho has warned that Manchester United face a “difficult season” unless they add reinforcements before the transfer window closes on Thursday.

United completed their pre-season programme with a 1-0 defeat to German champions Bayern Munich last night; Javi Martinez heading home the only goal of a game that the hosts dominated.

The Red Devils are understood to be preparing a bid for Leicester City defender Harry Maguire, however Mourinho would only say: “My CEO knows what I want and I still have a few days to wait and see what happens.

“The other clubs who compete with us are really strong and already have fantastic teams. Or they are investing massively like Liverpool, who are buying everything and everybody.

“If we don’t make our team better it will be a difficult season for us.”

Prior to the game, Mourinho and Ed Woodward were urged to put their heads together and bring the good times back by the club’s former chief executive Peter Kenyon.

Kenyon was a key figure at United during the glory years of Sir Alex Ferguson and has watched from a distance as the Red Devils have struggled to land the Premier League title for the past five years.

Their hopes of ending that sequence this term have not been helped by a pre-season dominated by Mourinho’s gloomy demeanour and clear frustration over transfers, an issue which places his relationship with executive vice-chairman Woodward in the spotlight.

Kenyon acknowledges things have yet to click two years into the Portuguese’s reign but does believe it can happen.

“They have to work it out and they’ll find a way of working it out,” he told BBC Radio 5 Live’s Sportsweek. “United is bigger than anybody, bigger than any individual and that’s always been the mantra.

“It will get worked out and I would hope Jose is part of that working it out because he is incredibly skilled and he’s demonstrated he can do things.

“He is more than capable, one of the best coaches in the world but have they got it right? No.

“I think the first people to recognise that will be the people at United.

“Jose has all the capabilities, he’s done it, but I don’t think he’s in a place where he feels good at the moment, or United feel good at the moment or the fans at the moment.”

Kenyon sees Manchester City’s rise as particularly difficult for United to deal with but is sure his old side have everything they need to close the gap on last year’s runaway champions.

“They’ve got more competition than they’ve ever had before and it’s coming from the other side of the city,” he said.